Recently, as the electronic appliances are becoming smaller in size and diversified in function, printed wiring boards widely used in such electronic appliances are required to be higher in wiring density and higher in reliability.
A conventional manufacturing apparatus used in forming conductor patterns in printed wiring boards, especially an etching apparatus is explained.
FIG. 21 is a schematic view of a conventional etching apparatus as a manufacturing apparatus of printed wiring boards. In FIG. 21, plural upper surface nozzle pipes 632 and plural lower surface nozzle pipes 633 disposed in an etching booth 641 are respectively provided with a plurality of spray nozzles 631.
An upper surface spray pump 638 supplies an etchant into an upper surface nozzle pipe 632 through an upper surface pressure regulating valve 636. A lower surface spray pump 639 supplies an etchant into a lower surface nozzle pipe 633 through a lower surface pressure regulating valve 637. The pressure of the etchant is checked respectively at an upper surface pressure gauge 634 and a lower surface pressure gauge 635. A feed roller 640 is used to convey a printed wiring board 642 in a running direction.
In the conventional etching apparatus having such structure, an etching method of printed wiring board is explained below.
First, a printed wiring board 642 forming an etching resist by screen printing method or photographic method on a copper lined laminate board (not shown) cut in specified size is conveyed into an etching booth 631 between plural upper surface nozzle pipes 632 and plural lower surface nozzle pipes 633 disposed parallel to or at a certain angle to the running direction of the printed wiring board 642, and conveyed on a roller 640 at a specified speed in the running direction, and sprayed with an etchant as a treating solution such as cupric chloride on both upper and lower surfaces by means of spray nozzles 631 to dissolve (etch) the exposed copper in the etching resist non-forming area, and a conductor pattern is obtained. At this time, the upper surface nozzle pipes 632 and lower surface nozzle pipes 633 can be oscillated at an angle of 45° to 60° to the running direction of the printed wiring board 642. Later, through the etching resist stripping, washing and drying steps, a conductor pattern is formed from the copper lined laminate board.
In such conventional etching apparatus and etching method, it is difficult to etch the copper precisely and uniformly on both upper and lower surfaces, and in particular the etching speed is likely to differ substantially between the upper surface and lower surface of the printed wiring board. That is, on the upper surface of the printed wiring board, deteriorated etchant containing much dissolved copper is likely to collect in the central area, but the deteriorated etchant in the peripheral area immediately flows down from the printed wiring board and is not collected, while on the lower surface of the printed wiring board, the etchant does not stay, and the fresh etchant having a high etching capability is always supplied on the lower surface.
As a result, a significant difference occurs in the etching precision of conductor pattern between the central area and peripheral area of the upper surface of the printed wiring board, and the difference is much greater between the upper surface and lower surface, and it is extremely difficult to etch the conductor pattern of printed wiring board of high density and high precision, and the process yield is extremely lowered, and this problem is more notable when the thickness of the printed wiring board is smaller and the density of the conductor pattern is higher.
To solve these problems, hitherto, it has been attempted to incline the printed wiring board or set upright, and inject the etchant from the spray nozzles in the horizontal direction, and various methods for eliminating retention of etchant have been proposed, but it is difficult to convey the printed wiring board and set the etching condition, and the productivity is significantly impaired, and the manufacturing cost of the manufacturing apparatus is soaring, and it is not widely employed at the present.